This invention relates to a mine roof support unit, and in particular to a mine roof support unit provided with an articulated goaf shield between a roof cap and a floor sill, at least one telescopic hydraulic prop being provided between the floor sill and the roof cap or between the floor sill and the goaf shield.
Roof support units of various designs are known in which each of the hydraulic props is pivotably mounted at its ends to the sill and the goaf shield or the roof cap. The pivotable mounts are such that each prop can pivot when extended or retracted, in a plane square to that of the floor sill and to that of the worked face. This causes a retracting prop to assume positions increasingly deviating from its desired position square to the floor sill. As a result, the supporting force of the props which is transmitted through the roof cap to the roof is considerably reduced. Where the props are intended to hold up the roof even when highly retracted, they do not always develop a sufficient force to underpin the roof safely.
The drawbacks arising from variable prop inclinations may be counteracted by overrating the props so that even when highly retracted, the roof is still held up with a sufficient force. However, while in the extended condition the supporting force of the props may then be too high and lead to undesirably excessive pressures upon the floor and sometimes on the roof. Moreover, oversize props must be used.
The main object of the invention is to provide a roof support unit which can hold up the roof of an underground working despite varying prop inclinations while highly retracted.
Another object is to provide a roof support unit which develops an adequate support force without oversize hydraulic props, and which may be laid out without transmitting unnecessary or even harmful supporting pressures to the roof while extended.
Yet another object is to provide a roof support unit in which the prop (s) is/are mounted between an overhanging (cantilever) roof cap pointing towards the work face and the floor sill in which the props may be highly inclined in operation.